The applicant and associated companies thereof have proposed a variety of actuators with a dustproof mechanism (including motion guidance apparatus that guide the motion of a traveling object) disclosed, for example, in the following Patent Documents 1 and 2. For example, the linear actuator with a dustproof mechanism proposed in Patent Document 1 is characterized by a function of reliably preventing dust from leaking through an opening of an actuator housing and a device provided on a movable stage and allowing a dustproof belt to detour in order to prevent the dustproof belt from interfering with a portion protruding from the movable stage in the opening of the actuator housing.
The linear actuator with a dustproof mechanism disclosed in the Patent Document 1 will be described with reference to FIG. 10. FIG. 10 describes the configuration of the linear actuator with a dustproof mechanism according to the related art, (a) in FIG. 10 being a top view of the linear actuator with a dustproof mechanism, (b) in FIG. 10 being a front view of the linear actuator with a dustproof mechanism, and (c) in FIG. 10 being a transverse cross-sectional view of the linear actuator with a dustproof mechanism.
As shown in FIG. 10, the linear actuator 1 with a dustproof mechanism according to the related art includes an elongated box-shaped housing member 2, a ball screw 3 rotatably supported in the housing member 2, a movable stage 4 that makes linear reciprocating motion in response to rotary motion of the ball screw 3, and a drive motor 5 for rotating the ball screw 3.
The housing member 2 includes a horizontal substrate 21, a pair of right and left vertical side plates 22, 23 standing vertically from the upper surface of the horizontal substrate and extending in parallel to the ball screw 3, and end blocks 24, 25 respectively attached to the front and rear ends of the vertical side plates 22, 23. One of the end blocks, the end block 24, rotatably supports one end of the ball screw 3. The other one of the end blocks, the end block 25, rotatably supports the other end of the ball screw 3, which passes through the block 25 and is connected to the drive motor 5.
Upper end portions of the right and left vertical side plates 22, 23 are bent inward at a right angle and form right and left horizontal upper plate portions 22a, 23a. A central partition plate 26 is disposed in between the right and left horizontal upper plate portions 22a, 23a, and the front and rear ends of the central partition plate 26 are fixed to the end blocks 24, 25, respectively. As a result, a left opening 27 extending in the axial direction of the ball screw 3, that is, the direction in which the movable stage 4 travels, is formed between the horizontal upper plate portion 22a and the central partition plate 26. Similarly, a right opening 28 is formed between the horizontal upper plate portion 23a and the central partition plate 26.
The openings 27, 28 are blocked with dustproof belts 29, 30, each being wider than the corresponding opening. The dustproof belts 29, 30 extend between the end blocks 24, 25 along the lower side of the horizontal upper plate portions 22a, 23a and the central partition plate 26.
As described above, the housing member 2 forms a box-shaped compartment surrounded by the horizontal substrate 21, the vertical side plates 22, 23 (horizontal upper plate portions 22a, 23a), the central partition plate 26, the end blocks 24, 25, and the dustproof belts 29, 30 that block the openings 27, 28. The housing member 2 thus covers the ball screw 3 and hence serves to keep dust produced from the actuator in the compartment.
The movable stage 4 includes a nut block 41 having a ball screw nut that engages the ball screw 3 formed therein, a lower plate 42 fixed to the upper surface of the nut block 41, an intermediate plate 43 fixed to the upper surface of the lower plate 42, and an upper plate 44 fixed to the upper surface of the intermediate plate 43. The side surfaces of the nut block 41 are supported by a linear guide rail 31 attached in the housing member 2 so that the nut block 41 can slide along the axial line of the ball screw 3.
The movable stage 4 is configured in such a way that the upper plate 44 is located outside the housing member 2 and the intermediate plate 43, the lower plate 42, and the nut block 41 are located inside the housing member 2. That is, the upper plate 44 protrudes out of the housing member 2 through the openings 27, 28, and, when connected to an object to be guided, can transmit a moving force to the object to be guided.
As the detouring device that allows the dustproof belts 29, to detour, rotatable rollers 61 to 66 are provided on the movable stage 4. The rollers 61 to 66 horizontally protrude from the portions of the right and left side surfaces of the movable stage 4 that are located in the housing member 2 and are disposed in such a way that the positions of the central rollers 63, 64 are lower than those of the other rollers 61, 62, 65, and 66, which are located on both end sides in the axial direction. (The roller 65 is disposed in a position opposite the position where the roller 66 is disposed, but is not shown in FIG. 10. The roller 65 is therefore presented in brackets in the following description.)
The dustproof belts 29, 30 engage the rollers 61 to 66 in such a way that the upper plate 44 protruding out of the housing member 2 through the openings 27, 28 does not interfere with the dustproof belts 29, 30. That is, the dustproof belts 29, 30 engage the rollers 61 to 66 in such a way that the dustproof belts 29, 30 run below the protruding portion of the upper plate 44 and detour the protruding portion. Specifically, the left dustproof belt 29 (the upper one in the plane of (a) of FIG. 10) engages the upper side of the front roller 61, the lower side of the central roller 63, and the upper side of the rear roller (65). Similarly, the right dustproof belt 30 (the lower one in the plane of (a) of FIG. 10) engages the upper side of the front roller 62, the lower side of the central roller 63, and the upper side of the rear roller 66.
Since the linear actuator 1 with a dustproof mechanism according to the related art is configured as described above, the openings 27, 28 formed along the path along which the movable stage 4 travels can be always blocked with the dustproof belts 29, 30. Dust produced, for example, when the ball screw nut in the nut block 41 slides along the ball screw 3 or when the nut block 41 slides along the linear guide rail will not leak out of the housing member 2 through the openings 27, 28 thereof.
Further in the linear actuator 1 with a dustproof mechanism according to the related art, since the dustproof belts 29, 30 are disposed inside the housing member 2 and the dustproof belts 29, 30 can run below the movable stage 4, which travels along the openings 27, 28, and detour the movable stage 4, the openings 27, 28 always remain blocked with the dustproof belts 29, 30 when the movable stage 4 travels.
The thus configured linear actuator 1 with a dustproof mechanism according to the related art further includes air inlets through which air is sucked out of the housing member 2. That is, housing air inlets 22b, 23b are formed in the pair of right and left vertical side plates 22, 23, as shown in FIG. 10, and the air in the housing member 2 can be sucked through the housing air inlets 22b, 23b. 
Further, air inlet ducts 7, 8 are attached to the horizontal upper plate portions 22a, 23a, which are formed at the upper ends of the vertical side plates 22, 23, and air inlets 7b, 8b for the narrow ducts extending along the openings 27, 28 are formed between the air inlet ducts 7, 8 and the horizontal upper plate portions 22a, 23a. The dust produced in the housing is therefore sucked through the housing air inlets 22b, 23b formed in the right and left vertical side plates 22, 23 to an external duct collector or any other suitable component (not shown) and removed out of the housing member 2.
In a clean room or any other similar space, an air flow traveling downward is typically formed. Therefore, when air is sucked through the air inlets 7b, 8b for the ducts disposed adjacent to the openings 27, 28, the dust having leaked through the openings 27, 28 is sucked through the air inlets 7b, 8b for the ducts along with the air traveling downward. The dust can therefore be reliably sucked and removed without being scattered into the atmosphere.
Patent Document 1: Japanese Patent Laid-Open No. 2000-266151
Patent Document 2: Japanese Patent Laid-Open No. 2005-188600